I have built multiple BB 33's over the last 3 years or so. Also been scratch building and flying most of my life (about 50 years????)

If you give your BB some extreme 20-30 degree throws, it can be twitchy, especially since it is Short Coupled, AND has a shotr wingspan. But I like mine that way. Short coupled, and a short and wide wingspan is all an important part of the design, and thousands of users have had so much fun and success with it.

I can snap roll mine with rudder/elevator only. It happens so fast and in about 2 or 3 airplane lengths of flight doing it! But with the high wing, the pendulum effect when self righting is a definite "twitchy' recovery. Turn up your control throws and experiance a lot more fun! Watch adding floats if you do because when it self rights out of a sharp banking turn, it will swing the undercarriage the opposite direction coming out of the turn!

Any short coupled airplane witll fly a bit more tame with a longer moment, and often a longer and thinner wing is recommended. You could also shrink the tail section sizes, but then we start to come up with a complete re-design. Keep it simple, but nothing is hurt by some small adjustments.

Fred

My Kfm3 33" blu baby snap rolls in a heartbeat and rolls like a drill with full width ailerons. Short coupling means it banks like crazy with rudder. Loops are possible at 1/3 throttle with 1700kv blue wonder on 3s. My throws are large, close to 45 degrees everywhere except ailerons which I set up differential on via my Dx8. But - let off the controls it doesn't right itself because of no dihedral but it absolutely STOPS flopping around the sky. For what it is it's ridiculously aerobatic. It's a great plane, I love it.

My Kfm3 33" blu baby snap rolls in a heartbeat and rolls like a drill with full width ailerons. Short coupling means it banks like crazy with rudder. Loops are possible at 1/3 throttle with 1700kv blue wonder on 3s. My throws are large, close to 45 degrees everywhere except ailerons which I set up differential on via my Dx8. But - let off the controls it doesn't right itself because of no dihedral but it absolutely STOPS flopping around the sky. For what it is it's ridiculously aerobatic. It's a great plane, I love it.

Now we're talking! Tons of fun from one simple little foamie aircraft design.

Images

Not familiar with the eflite motor, but if it's about a 40gm motor at 1200kv then you are in the ballpark, but the 7x4 prop sounds a bit small, the smallest I use on my 42" span BB is an 8x6, and more usually go to a 9". It'll fly with a lot bigger battery too, of course. depending on where you put the pack, that may help your balance as well.

The plane is tail heavy but I'm still trying to balance (so far it balances after adding dummy 25 gms after the motor!).

What do you think?

andalosy:

One of the most common causes of crashed RC airplanes is the center of gravity, CG, not being properly placed. The weight you're adding is anoying but important.
Most importantly, make sure the CG is NOT AFT (rear of) of the recommended 3.44 inches (87mm) from the leading edge of the wing just next to the fuselage shown in the Blu Baby 42 inch KFm3 World Plan.pdf in post #107

Not familiar with the eflite motor, but if it's about a 40gm motor at 1200kv then you are in the ballpark, but the 7x4 prop sounds a bit small, the smallest I use on my 42" span BB is an 8x6, and more usually go to a 9". It'll fly with a lot bigger battery too, of course. depending on where you put the pack, that may help your balance as well.

I use a 370 park motor on my 42", with a 10" prop. I maidened with a 9" and 3s 800marh battery. Which flew well, but the 10 is better and I prefer using 3s 1300mah batteries as well. It allows better penetration in wind, bigger might still be better, but that's all I have. As noted by others make sure you get your C.G. right and mark where your battery is placed so you don't accidentally change it when you change/charge your batteries.

Images

Looks good, I think you're gonna like her! (I was gonna comment to not forget to consider skis and floats in addition to wheels for future activities with your new plane, before I noticed where you're located! - maybe floats if you're close to the ocean, but I doubt you'll need skis)

Looks good, I think you're gonna like her! (I was gonna comment to not forget to consider skis and floats in addition to wheels for future activities with your new plane, before I noticed where you're located! - maybe floats if you're close to the ocean, but I doubt you'll need skis)

I use a 370 park motor on my 42", with a 10" prop. I maidened with a 9" and 3s 800marh battery. Which flew well, but the 10 is better and I prefer using 3s 1300mah batteries as well. It allows better penetration in wind, bigger might still be better, but that's all I have. As noted by others make sure you get your C.G. right and mark where your battery is placed so you don't accidentally change it when you change/charge your batteries.

Hi sixfins,

I just finished testing the park 370 with a 9x4 prop and it seems beyond the motor capability (Watt meter reads 11 amp at 85-90% throttle!). Would you please give more details about the type and pitch of the propeller you used?

I think it was a 9x6, can't really remember. What I use now are 10x4.7 and 10x6. I think they are GWS props, not sure. They're the cheapest ones at my LHS only $1 each. Really I only use about half throttle most of the time. With full throttle I have unlimited vertical and can take of with only a few inch roll out if any (well under 1'). With half throttle I can do loops and rolls, fly inverted and land after 8-10 minutes. The motor is always cool, not even warm, the esc and battery get warm, but not hot (about 95-97°).